Understanding changes in precipitation with climate change over wet and dry land

Abstract

Observed precipitation increased moderately in both wet and dry regions over the past 60 years, contradicting the wet-gets-wetter, dry-gets-drier (WWDD) mechanism. This study uses the perturbation atmospheric energy budget to understand the projected increase in precipitation over dry and wet land with climate change. Using global climate model output, the change in each term in the perturbation energy budget was calculated as a regional average over wet and dry tropical land. Increases in precipitation over wet and dry tropical land are primarily driven by increases in radiative loss, which are moderated by increases in sensible heat flux. Although the dry static energy flux divergence has a strong spatial pattern, cancellation between the horizontal and vertical advection terms, as well as cancellation between the dynamic and thermodynamic components of vertical advection, result in relatively small contributions from the dry static energy flux divergence towards the change in precipitation in the regional average. Only when wet and dry regions are allowed to change seasonally is WWDD given, suggesting that the movement of wet and dry regions is a significant factor in opposing the WWDD mechanism over land.